In the continuing development of valve actuators, the direction of such development has been toward a modular design utilizing field serviceable modules, including the power, the drive, and the spring return modules. Of paramount concern is the safety of the user. The spring may be under such compression as to store enormous forces, for example, some spring return modules of the type described herein produce spring torques in excess of 3,000,000 lb.-in. For the safety of those servicing these actuators, outside of a workshop, and persons nearby, it is essential that any stored energy in the spring not be released so as to turn any module components ballistic. To accomplish this safety feature is a principal purpose of this invention. This purpose is accomplished by locking the spring module in place while it is under load.